Process for the preparation of ethyl acetate

ABSTRACT

Ethanol is dehydrogenated in the presence of hydrogen over a dehydrogenation catalyst, for example, a copper on silica catalyst. The liquefiable products present in the resulting intermediate reaction product mixture are selectively hydrogenated over a suitable catalyst, such as 5% ruthenium on carbon, so as selectively to hydrogenate reactive carbonyl-containing by-products to the corresponding alcohols. Butan-2-one and n-butyraldehyde are thereby hydrogenated to 2-butanol and n-butanol respectively. A two stage distillation procedure is then used to purify the selectively hydrogenated product. A first distillate of ethyl acetate, ethanol and water produced in the first distillation zone is redistilled in the second distillation zone, thereby producing a bottom product comprising, typically, from about 99.8 mol % to about 99.95 mol % ethyl acetate and an overhead second distillate, which has a different composition from that produced in the first distillation zone and which is returned to the first distillation zone.

This application was filed under 35 U.S.C. 371, and is the U.S. NationalStage of PCT/GB99/03230, filed Sep. 29, 1999.

This invention relates to a process for the production of ethyl acetate.

Etyl acetate is a relatively expensive bulk chemical which isconventionally produced by esterification of acetic acid with ethanolaccording to equation (1):

CH₃.CO.OH+CH₃CH₂OH═CH₃.CO.O.CH₂.CH₃+H₂O  (1).

Because this reaction does not tend to lead to formation of by-productswhich have boiling points close to that of ethyl acetate, recovery ofsubstantially pure ethyl acetate from the esterification product mixtureis usually not complicated by the presence of by-products of theesterification reaction.

Some other methods which have been proposed for the conversion ofethanol to ethyl acetate, however, tend to lead to formation ofby-products, notably n-butyraldehyde and butan-2-one, which have boilingpoints close to that of ethyl acetate and hence make the recovery ofsubstantially pure ethyl acetate from the resulting reaction productmixtures more difficult than from esterification reaction mixtures.These methods include dehydrogenation of ethanol, oxidation of ethanol,reaction of ethanol with acetaldehyde, and oxidation of ethanol toacetaldehyde followed by the Tischenko reaction.

Ethyl acetate can be produced from acetaldehyde according to theTischenko reaction given in equation (2):

2CH₃.CHO═CH₃.CO.O.CH₂.CH₃  (2).

It is also possible to produce ethyl acetate from ethanol bydehydrogenation according to equation (3):

2CH₃.CH₂.OH═CH₃.CO.O.CH₂.CH₃+2H₂  (3).

According to China Chemical Reporter, 26 Mar. 1996, a plant with acapacity of 5000 tonnes per annum for production of ethyl acetate bydehydrogenation of ethanol has been constructed at Linshu ChemicalFertilizer Plant of Shandong using a catalyst developed by QinghuaUniversity.

Ethanol is produced in large quantity by a variety of processes,including hydration of ethylene, the Fischer Tropsch process, or as afermentation product. The purity of the ethanol often depends upon themethod used for its production. For example, although hydration ofethylene yields a substantially pure ethanol product, the FischerTropsch process yields also a number of by-products which aretroublesome to remove from the ethanol product. In the case offermentation, the ethanol product is obtained as an aqueous solutionwhich may also contain by-products whose removal from the ethanol isdifficult.

In certain circumstances ethanol may be available in excess capacity,whilst acetic acid is not readily available in the necessary quantity.Accordingly, there are many reasons why, particularly in countrieshaving a relative abundance of ethanol with respect to acetic acid, itis commercially interesting to produce ethyl acetate from ethanol,acetaldehyde or a mixture thereof.

Catalytic dehydrogenation of alcohols with reduced copper under ultraviolet light was described by S. Nakamura et al, in Bulletin of theChemical Society of Japan (1971), Vol. 44, pages 1072 to 1078.

K. Takeshita et al described reduced copper catalysed conversion ofprimary alcohols into esters and ketones in Bulletin of the ChemicalSociety of Japan, (1978) Vol. 51(9), pages 2622 to 2627. These authorsmention that the mechanism for ester formation has been described in theliterature as the Tischenko reaction. That is to say thatdehydrogenation of ethanol yields acetaldehyde as an intermediate whichcombines according to the Tischenko reaction to produce ethyl acetate.Alternatively, or as well, 1 mole of ethanol may combine with 1 mole ofacetaldehyde to yield 1 mole of ethyl acetate and 1 mole of hydrogenaccording to equation (4)

CH₃CH₂OH+CH₃.CHO═CH₃.CO.O.C₂.CH₃+H₂  (4).

U.S. Pat. No. 4,996,007 teaches a process for the oxidation of primaryalcohols to aldehydes, acids and esters, particularly to aldehydes. Inthis process a primary alcohol is contacted, together with molecularoxygen, with a catalyst selected from ruthenium, rhodium, platinum,palladium, rhenium and mixtures thereof, optionally a quaternary C₁ toC₂₀ alkyl ammonium cocatalyst, and as oxygen activatordihydrodihydroxynaphthalene, dihydrodihydroxyanthracene or a mixturethereof. The product aldehydes, acids and esters are then separated fromthe reaction mixture.

In U.S. Pat. No. 4,220,803 catalytic dehydrogenation of ethanol for theproduction of acetaldehyde and acetic acid using a supported copperoxide essentially free of barium is proposed.

A silver-cadmium alloy catalyst has been suggested for use in productionof alkyl alkanoate esters, by contacting a primary alkanol in the vapourphase with the catalyst at a temperature of between about 250° C. and600° C., in U.S. Pat. No. 4,054,2424.

In U.S. Pat. No. 4,440,946 there is described a process for producing acarboxylate ester which comprises contacting a mixture of alcohol andaldehyde in the vapour phase with a coprecipitate composition comprisingsilver-cadmium-zinc-zirconium which is substantially in the free metalform.

Use of the Tischenko reaction for the production of mixed esters fromaldehydes is described in U.S. Pat. No. 3,714,236.

U.S. Pat. No. 5,334,751 teaches production of ethyl acetate by reactionof ethanol and oxygen in the presence of a solid catalyst that containscrystalline TiP₂O₇ and has the formula Pd_(a)M_(b)TiP_(c)O₇, where M isCd, Au, Zn, Tl, or an alkali metal or alkaline earth metal, a is0.0005-0.2, b is 0.3a, c is 0.5-2.5, x has a value to satisfy thevalencies, and Ti and P of the crystalline TiP₂O₇ represent part of thecrystalline TiP₂O₇.

BR-A-91/04652 teaches pre-treatment of a palladium on a silica carriercatalyst for production of ethyl acetate by direct oxidation of ethanolwith air.

Production of esters from primary alcohols by dehydrogenation usingbromous acid or a salt thereof in acid medium is described inJP-A-59/025334.

In SU-A-362814 there is described a process for production of ethylacetate by dehydrogenation of ethanol at 180° C. to 300° C. in thepresence of a copper catalyst containing zinc as an activator with anethanol feed rate of 250 to 700 liters per liter of catalyst per hour.

The dehydrogenation of ethanol to form ethyl acetate is described inGB-A-287846. This proposes use of a dehydrogenating agent, such as acopper catalyst, a temperature of from 250° C. to 500° C., and apressure of more than 10 atmospheres (1.013×10⁶ Pa).

Vapour phase contact of ethanol at a temperature above its criticaltemperature with a catalyst comprising copper and a difficultlyreducible oxide, such as zinc oxide or manganese oxide, is proposed inGB-A-312345, use of a temperature of 375° C. and a pressure of 4000 psi(27.58 Mpa) being suggested.

GB-A-470773 teaches a process for conversion of ethanol to ethyl acetateby dehydrogenating ethanol over a catalyst consisting of a reducedmetal, for example, copper on infusorial earth with 10% uranium oxide aspromoter, maintained at a temperature of 220° C. to 260° C., removing bycondensation some of the gas-vapour product rich in hydrogen resultingfrom the reaction, and returning the gaseous remainder rich in hydrogento the catalysing zone.

EP-A-0151886 describes a process for the preparation of C₂₊ esters ofalkyl carboxylic acids from C₂₊ primary alcohols which comprisescontacting a vaporous mixture containing a primary C₂₊ alkanol andhydrogen in an alkanol:hydrogen molar ratio of from 1:10 to about 1000:1at a combined partial pressure of alkanol and hydrogen of from about 0.1bar (10³ Pa) up to about 40 bar (4×10⁶ Pa) and at a temperature in therange of from about 180° C. to about 300° C. in a catalytic reactionzone with a catalyst consisting essentially of a reduced mixture ofcopper oxide and zinc oxide, and recovering a reaction product mixturecontaining a primary C₂₊ alkyl ester of an alkyl carboxylic acid whichester contains twice as many carbon atoms as the primary C₂₊ alkanol.

In EP-A-0201105 there is described a method for converting primaryalcohols, such as ethanol, to their corresponding alkanoate esters whichinvolves the regulation of the mole feed ratio of hydrogen gas toalkanol in the reaction zone of a copper chromite containing catalyst.

One method of separating ethyl acetate from ethanol and water involvesextractive distillation with an extractive agent comprising polyethyleneglycol and dipropylene glycol, diethylene glycol, or triethylene glycolas described in U.S. Pat. No. 4,569,726 or with an extractive agentcontaining dimethyl sulphoxide as described in U.S. Pat. No. 4,379,028.

Separation of ethyl acetate from a composition comprising ethyl acetate,ethanol and water is disclosed in JP-A-05/186392 by feeding thecomposition to a distillation column to obtain a quasi-azeotropicmixture comprising ethyl acetate, ethanol and water, condensing it,separating the condensate into an organic layer and an aqueous layer,returning the organic layer to the column, and recovering ethyl acetateas a bottom product from the column.

EP-A-0331021 describes how carbonylation of olefins to producemonocarboxylate esters causes formation of aldehydes and acetals asbyproducts. Monocarboxylate esters produced in this way are subjected toa three step purification process involving treatment with a stronglyacidic agent, followed by hydrogenation and distillation. The initialtreatment with a strongly acidic agent is intended to convert acetals tovinyl ethers and aldehydes and acetals to aldols. The subsequenthydrogenation step then converts these compounds to byproducts which aremore easily separated from the desired monocarboxylate ester.

EP-A-0101910 contains a similar disclosure regarding carbonylation ofolefins to give monocarboxylate esters. It proposes treatment of themonocarboxylate ester with hydrogen at elevated temperature in thepresence of an acidic ion exchanger or zeolite doped with one or moremetals of Group VIII of the Periodic Table, followed by hydrogenation.It is stated that acetals present as byproducts are converted to vinylethers which are converted by hydrogenation to low boiling esters or thealdehydes and acetals are converted to high boilers by an aldolreaction. Unsaturated ketones are converted to saturated ketones.

It would be desirable to provide an improved commercial method ofupgrading ethanol to ethyl acetate, a more valuable product,particularly where there is an over-capacity for ethanol. It would alsobe desirable to provide a novel route to high purity ethyl acetate whichobviates the need for a separate acetaldehyde or acetic acid plant. Itwould further be desirable to provide a process for the production ofsubstantially pure ethyl acetate directly from ethanol without the needto convert part of the ethanol feedstock to acetaldehyde or to aceticacid. Additionally it would be desirable to provide a route to ethylacetate by dehydrogenation of ethanol which is capable to yielding highpurity ethyl acetate from ethanol feed streams containing significantamounts of impurities.

One particular problem in production of ethyl acetate by dehydrogenationof ethanol is that the reaction product mixture tends to be a complexmixture including esters, alcohols, aldehydes and ketones. The reactionmixture can be even more complex when the ethanol feed containsimpurities. The reaction product mixtures contain components withboiling points close to ethyl acetate (such as U-butyraldehyde andbutan-2-one), including components which can form azeotropes with ethylacetate, and/or other components of the mixture. This is a particularproblem when high purity ethyl acetate is desired. Another problem isthat water present in the feed ethanol or produced as a by-productduring dehydrogenation has a deactivating effect on dehydrogenationcatalysts so that any recycle to the dehydrogenation reactor ofunconverted ethanol should desirably contain only a low level, if any,of water.

The present invention accordingly seeks to provide a novel process forproduction of ethyl acetate from ethanol, enabling production of ethylacetate at a relatively low cost and involving simple plant. Anotherobject of the present invention is to provide an improved process forthe production of high purity ethyl acetate from ethanol, or from afeedstock comprising a major proportion of ethanol and a minorproportion of impurities such as iso-propanol.

According to the present invention there is provided a process for theproduction of ethyl acetate which comprises:

(a) converting a C₂ feedstock comprising ethanol to ethyl acetate in anethyl acetate production zone by a procedure selected from:

(i) dehydrogenation,

(ii) oxidation,

(iii) reaction with acetaldehyde, and

(iv) oxidation to acetaldehyde followed by the Tischenko reaction;

(b) recovering from the ethyl acetate production zone an intermediatereaction product mixture comprising hydrogen and liquefiable productscomprising ethyl acetate, ethanol, and by-products containing reactivecarbonyl groups;

(c) contacting at least a portion of the liquefiable products of theintermediate reaction product mixture with a selective hydrogenationcatalyst in the presence of hydrogen in a selective hydrogenation zonemaintained under selective hydrogenation conditions effective forselective hydrogenation of by-products containing reactive carbonylgroups thereby to hydrogenate said by-products selectively tohydrogenated by-products comprising corresponding alcohols;

(d) recovering from the selective hydrogenation zone a selectivelyhydrogenated reaction product mixture comprising ethyl acetate, ethanol,hydrogen and hydrogenated by-products;

(e) distilling material of the selectively hydrogenated reaction productmixture in one or more distillation zones so as to produce a firstcomposition comprising substantially pure ethyl acetate and a secondcomposition comprising ethanol and water;

(f) treating the second composition of step (e) to separate watertherefrom and yield a third composition comprising ethanol with areduced water content; and

(g) recovering the third composition of step (f).

In step (a) of the process of the invention the C₂ feedstock isconverted to ethyl acetate by (i) dehydrogenation, (ii) oxidation, (iii)reaction with acetaldehyde, or (iv) oxidation to acetaldehyde followedby the Tischenko reaction. In all-of these processes by-products of thereaction include C₄ compounds having boiling points which are close tothat of ethyl acetate (b.p. 77.1° C.) and hence give rise to problems inpurification of the ethyl acetate product. Notable amongst theseby-products are butane-2-one (b.p. 79.6° C.) and n-butyraldehyde (b.p.75.7° C.). Such by-products are not produced in the course of productionof ethyl acetate by esterification of ethanol with acetic acid.

The C₂ feedstock used instep (a) comprises ethanol which has beenproduced by hydration of ethylene, by the Fischer Tropsch process, or byfermentation of a carbohydrate source, such as starch. It mayalternatively be a byproduct of another industrial process. It maycontain, besides ethanol, minor amounts of water as well as smallamounts of impurities resulting from byproduct formation during itssynthesis. If the C₂ feedstock includes recycled unreacted ethanol, thenany by-products formed in the dehydrogenation step which are containedin the recycled ethanol will also contribute to the level of by-productspresent in the C₂ feedstock. Impurities present in the C₂ feedstock mayinclude, for example, higher alcohols such as n-propanol, iso-propanol,n-butanol and sec-pentanol; ethers, such as diethyl ether, anddi-iso-propyl ether; esters, such as iso-propyl acetate, s-butyl acetateand ethyl butyrate; and ketones, such as acetone, butan-2-one, and2-pentanone. At least some of these impurities can be difficult toremove from ethyl acetate, even when they are present in quantities aslow as about 0.1 mol % or less, by traditional distillation proceduresbecause they have boiling points which are close to that of ethylacetate and/or form constant boiling mixtures therewith.

In step (a) the C₂ feedstock may be subjected to dehydrogenationaccording to equation (3) above. In this case the C₂ feedstock can beconverted to ethyl acetate by a dehydrogenation procedure whichcomprises contacting a vaporous mixture containing ethanol and hydrogenwith a dehydrogenation catalyst in a dehydrogenation zone maintainedunder dehydrogenation conditions effective for dehydrogenation ofethanol to yield ethyl acetate.

Typical dehydrogenation conditions include use of an ethanol:hydrogenmolar ratio of from about 1:10 to about 1000:1, a combined partialpressure of ethanol and hydrogen of up to about 50 bar (5×10⁶ Pa), and atemperature in the range of from about 100° C. to about 260° C.

Preferably the combined partial pressure of ethanol and hydrogen rangesfrom about 3 bar (3×10⁵ Pa) up to about 50 bar (5×10⁶ Pa), and is morepreferably at least 6 bar (6×10⁵ Pa) up to about 30 bar (3×10⁶ Pa), andeven more preferably in the range of from about 10 bar (10⁶ Pa) up toabout 20 bar (3×10⁶ Pa), for example from about 12 bar (1.2×10⁶ Pa) toabout 15 bar (1.5×10⁶ Pa).

Dehydrogenation is preferably conducted in the dehydrogenation zone at atemperature of from about 200° C. to about 250° C., preferably at atemperature in the range of from about 210° C. to about 240° C., evenmore preferably at a temperature of about 220° C.

The ethanol:hydrogen molar ratio in the vaporous mixture fed intocontact with the dehydrogenation catalyst usually will not exceed about400:1 or about 500:1 and may be no more than about 50:1.

The dehydrogenation catalyst is desirably a catalyst containing copper,optionally in combination with chromium, manganese, aluminium, zinc,nickel or a combination of two or more of these metals, such as acopper, manganese and aluminium containing catalyst. Preferred catalystscomprise, before reduction, copper oxide on alumina, an example of whichis the catalyst sold by Mallinckrodt Specialty Chemicals, Inc., underthe designation E408Tu, a catalyst which contains 8% by weight ofalumina. Other preferred catalysts include chromium promoted coppercatalysts available under the designations PG85/1 (Kvaerner ProcessTechnology Limited) and CU0203T (Engelhard), manganese promoted coppercatalysts sold under the designation T4489 (Sud Chemie AG), andsupported copper catalysts sold under the designation D-32-J (Sud ChemieAG). E408Tu is a particularly preferred dehydrogenation catalyst.

In the dehydrogenation step the rate of supply of the C₂ feedstock tothe dehydrogenation zone typically corresponds to an ethanol liquidhourly space velocity (LHSV) of from about 0.5 hr⁻¹ to about 1.0 hr⁻¹.

Hydrogen is produced as a result of the dehydrogenation reaction and canbe recycled to the dehydrogenation zone from downstream in the process.The hydrogen can be substantially pure hydrogen or can be in the form ofa mixture with other gases that are inert to the C₂ feedstock and to thedehydrogenation catalyst. Examples of such other gases include inertgases such as nitrogen, methane and argon.

In the dehydrogenation zone, side reactions may also occur, includingformation of water. It is postulated that such side reactions includeformation of acetaldehyde which in turn can undergo aldol formation,followed by dehydration to form an unsaturated alcohol and water. Thesereactions can be summarised thus:

CH₃CH₂OH═CH₃CHO+H₂  (5)

2CH₃CHO═CH₃CH(OH)CH₂CHO  (6) and

CH₃CH(OH)CH₂CHO═CH₃CH═CHCHO+H₂O  (7).

The crotonaldehyde produced by equation (7) can then undergohydrogenation to form 2-butanol thus:

CH₃CH=CHCHO+H₂=CH₃CH₂CH₂CH₂OH  (8).

Other side reactions which release water as a by-product includeformation of ketones, such as acetone and butan-2-one, and formation ofethers, such as diethyl ether.

It is alternatively possible to subject the C₂ feedstock to oxidation inorder to effect production of ethyl acetate as taught by U.S. Pat. No.5,334,751 or by U.S. Pat. No. 4,996,007.

Alternatively the C₂ feedstock can be passed in admixture with air overa palladium on a silica carrier catalyst thereby to produce ethylacetate by direct oxidation of ethanol with air as taught byBR-A-91/04652.

Yet another method of effecting oxidation of the C₂ feedstock so as toproduce ethyl acetate is to use bromous acid or a salt thereof in acidmedium as described in JP-A-59/025334.

Yet another method of converting the C₂ feedstock to ethyl acetate is toreact it with acetaldehyde to yield ethyl acetate and hydrogen accordingto equation (4) above.

Still another method of converting the C₂ feedstock to ethyl acetateinvolves oxidation of ethanol to acetaldehyde, for example by theprocess of U.S. Pat. No. 4,220,803, followed by conversion of theacetaldehyde product to ethyl acetate by the Tischenko reaction ofequation (2) above. Typical Tischenko reaction conditions are set out inU.S. Pat. No. 3,714,236. Again water can be a by-product of thisreaction, being formed, it is postulated, by equations (6) and (7)above.

In step (b) of the process of the invention there is recovered from theethyl acetate production zone an intermediate reaction product mixturecomprising hydrogen and liquefiable products comprising ethyl acetate,ethanol, water, and by-products containing reactive carbonyl groups.This step can be effected in any convenient manner and may include acondensation step in order to condense liquefiable products present inthe intermediate reaction product mixture. Alternatively theintermediate reaction product can be passed directly to step (c) withoutany intermediate condensation step.

A range of undesirable by-products may be present in the intermediatereaction product mixture, some of which would cause separation problemsif the intermediate reaction product mixture were to be directly refinedbecause their boiling points are close to that of ethyl acetate orbecause they form azeotropes with ethyl acetate whose boiling point isclose to that of ethyl acetate. Such by-products may be present in theC₂ feedstock or may be produced in step (c). Problematical by-productsare aldehydes and ketones, such as n-butyraldehyde and butan-2-one. Inorder to avoid problems due to the presence of such by-products in thedistillation step (e), even in amounts as small as about 0.1 mol % orless, e.g. about 0.01 mol % or less, the problematical by-products aresubstantially removed as a result of the selective hydrogenation step(c). Accordingly, liquefiable products present in the intermediatereaction product mixture of step (b) are reacted in step (c) withhydrogen over a suitable selective hydrogenation catalyst. The catalysttype and reaction conditions are chosen so that aldehydes and ketonesare hydrogenated to their respective alcohols, while hydrogenation ofethyl acetate is minimal. Among aldehyde and ketone by-products whichmay be present, butan-2-one and n-butyraldehyde, in particular, wouldotherwise cause problems in any subsequent distillation. These compoundsare hydrogenated in the selective hydrogenation zone in step (c) to thecorresponding alcohols, i.e. 2-butanol and n-butanol respectively, whichcan be readily separated from ethyl acetate by distillation.

The mixture supplied to the selective hydrogenation zone in step (c)contains, in addition to ethanol, hydrogen either alone or in admixturewith one or more inert gases that are inert to the reactants andcatalysts in the selective hydrogenation step (c) of the process of theinvention. Examples of such inert gases have been given above. Thesource of the hydrogen used in the selective hydrogenation step (c) maybe hydrogen formed in the dehydrogenation step and may include gasrecycled from the downstream end of the selective hydrogenation zone.

The selective hydrogenation step (c) is typically conducted at atemperature of from about 20° C. to about 160° C., preferably at atemperature in the range of from about 40° C. to 120° C., even morepreferably at a temperature of about 60° C. to about 80° C. Typicalselective hydrogenation conditions include use of a reaction productmixture:hydrogen molar ratio of from about 1000:1 to about 1:1,preferably from about 100:1 to about 5:1, for example about 20:1.

The combined partial pressure of liquefiable products and hydrogen inthe selective hydrogenation zone typically lies in the range of fromabout 5 bar (5×10⁵ Pa) up to about 80 bar (8×10⁶ Pa), and is even moretypically from about 25 bar (2.5×10⁶ Pa) to about 50 bar (5×10⁶ Pa).

The selective hydrogenation catalyst used in step (c) of the process ofthe invention is selected to have good activity for hydrogenation ofreactive carbonyl containing compounds, but relatively poor esterhydrogenation activity. Suitable catalysts comprise metals selected fromnickel, palladium and platinum. Ruthenium, supported on carbon, aluminaor silica is also effective, as are other metal catalysts such asrhodium and rhenium. Preferred catalysts include nickel on alumina orsilica and ruthenium on carbon. Particularly preferred catalysts include5% ruthenium on carbon available from Engelhard.

The rate of supply of liquefiable liquid products of the intermediatereaction product mixture to the selective hydrogenation zone dependsupon the activity of the selective hydrogenation catalyst but typicallycorresponds to a liquid hourly space velocity (LHSV) of from about 0.1hr⁻¹ to about 2.0 hr⁻¹, preferably from about 0.2 hr⁻¹ to about 1.5hr⁻¹. When using, for example, a ruthenium on carbon catalyst the LHSVmay be from about 0.5 hr⁻¹ to about 2.0 hr⁻¹, for example from about 1.0hr⁻¹ to about 1.5 hr⁻¹. When using a nickel containing catalyst the LHSVmay be, for example, from about 0.3 hr⁻¹ to about 0.5 hr³¹ ¹.

Step (d) of the process of the present invention comprises recoveringfrom the selective hydrogenation zone a selectively hydrogenatedreaction product mixture comprising ethyl acetate, ethanol, hydrogen andhydrogenated by-products. Typically this includes a condensation step inorder to separate liquefiable materials from a gaseous stream containingunreacted hydrogen which can be recycled for dehydrogenation or forselective hydrogenation.

Step (e) of the process of the invention comprises distilling materialof the selectively hydrogenated reaction product mixture in one or moredistillation zones so as to produce a first composition comprisingsubstantially pure ethyl acetate and a second composition comprisingethanol and water. In this step the material subjected to distillationtypically has a water content of less than about 20 mol %, more usuallynot more than about 15 mol %.

Ethanol, water and ethyl acetate form a minimum boiling ternaryazeotrope upon distillation thereof.

Step (e) may comprise an extractive distillation procedure as describedin U.S. Pat. No. 4,569,726 or in U.S. Pat. No. 4,379,028.

Preferably, however, distillation is carried in step (e) by a procedurewhich takes advantage of the fact that the composition of the minimumboiling ternary azeotrope formed by ethanol, water and ethyl acetatedepends upon the pressure at which distillation is effected. Hence apreferred distillation procedure comprises supplying material of theselectively hydrogenated reaction product mixture to a firstdistillation zone maintained under distillation conditions effective fordistillation therefrom of a first distillate comprising ethyl acetate,ethanol, and water, recovering a first distillate comprising ethylacetate, ethanol, and water from the first distillation zone and abottom product comprising ethanol and water, supplying material of thefirst distillate to a second distillation zone maintained underdistillation conditions effective for distillation therefrom of a seconddistillate comprising ethanol, water, and ethyl acetate (typically aminor amount of ethyl acetate) and so as to yield a substantially pureethyl acetate bottom product, and recovering a substantially pure ethylacetate bottom product from the second distillation zone. The firstdistillation zone is preferably operated at a pressure less than about 4bar (4×10⁵ Pa), preferably from about 1 bar (10⁵ Pa) up to about 2 bar(2×10⁵ Pa), while the second distillation zone is operated at a higherpressure than that of the first distillation zone, for example at apressure of from about 4 bar (4×10⁵ Pa) to about 25 bar (2.5×10⁶ Pa),preferably from about 9 bar (9×10⁵ Pa) to about 15 bar (15×10⁵ Pa).

It can be shown that in this preferred distillation procedure the rateof flow of the first distillate from the first distillation zone to thesecond distillation zone and the corresponding flow rate from the seconddistillation zone to the first distillation zone of the seconddistillate can be minimised by operating one of the distillation zonesso that the distillate has a composition very close to that of theternary azeotrope at that pressure. However, in order to operate thatzone so that the distillate has a composition close to that of theternary azeotrope at its pressure of operation, a high degree ofseparation is required which necessitates use of a column with manydistillation trays and a high heat input. In addition, since water hasthe highest latent heat of vaporisation out of the three components ofthe ternary azeotrope, the total heat input to the two zones can beminimised by minimising the water content of the feeds to thedistillation zones.

In addition to forming a ternary azeotrope, the three components of theternary azeotrope can also form binary azeotropes with one of the othercomponents. For example, ethanol forms a binary azeotrope with water andalso with ethyl acetate. It is preferred to select a pressure ofoperation of the second distillation zone so that the binary azeotropebetween ethanol and ethyl acetate at that pressure has a lower ethylacetate content than the ternary azeotrope at that pressure and furtherto select a pressure of operation for the first distillation zone and toadjust the flow rates of the distillates between the first and secondzones so that the first distillate has as low a water content aspossible. In this way the second distillate recovered from the seconddistillation zone will have a low content of ethyl acetate.

In the preferred distillation procedure an ethanol rich streamcontaining substantially all of the water in the selectivelyhydrogenated reaction product mixture is recovered from the bottom ofthe first distillation zone, while an overhead stream that contains“light” components present in the selectively hydrogenated reactionproduct mixture is recovered from the first distillation zone, and thefirst distillate comprises a liquid draw stream which is recovered froman upper region of the first distillation zone and which comprises ethylacetate, ethanol, water and minor amounts of other components. By theterm “light” components is meant components that have lower boilingpoints than ethyl acetate and its azeotropes with water and ethanol. Theliquid draw stream typically contains less than about 10 mol % water.For example, it suitably comprises from about 1 mol % to about 6 mol %water, from about 40 mol % to about 55 mol % ethyl acetate, not morethan about 2 mol % minor products (preferably not more than about 1 mol% minor products) and the balance ethanol. Thus it may typically containabout 45 mol % ethyl acetate, about 50 mol % ethanol, about 4 mol %water and about 1 mol % other components. This liquid draw stream ispassed to the second distillation zone. The second distillate, with atypical composition of about 25 mol % ethyl acetate, about 68 mol %ethanol, about 6 mol % water, and about 1 mol % other components, isrecovered as an overhead stream from the second distillation zone, whilea bottom product comprising ethyl acetate is recovered from the seconddistillation zone which typically contains from about 99.8 mol % toabout 99.95 mol % ethyl acetate; this second distillate is returned tothe first distillation zone, preferably at a point above the feed pointof the liquefiable products of the selectively hydrogenated reactionproduct mixture.

The overhead stream from the first distillation zone contains “light”components present in the intermediate reaction product mixture, such asdiethyl ether, acetaldehyde and acetone. It can be burnt as a fuel.

In step (f) of the process of the invention the ethanol rich streamrecovered from the bottom of the first distillation zone is subjected totreatment for the removal of water therefrom thereby to produce arelatively dry ethanol stream which is suitable for recycle to step (a),if desired. This ethanol rich stream will contain any “heavies”, i.e.products, including unknown products, with high boiling points comparedto those of ethanol and ethyl acetate. These can be separated from theethanol and water by distillation, if desired, prior to effectingremoval of water from the resulting distillate. One suitable method forremoval of water from the ethanol rich stream or from the distillateresulting from “heavies” removal is molecular sieve adsorption.Azeotropic distillation with a suitable entrainment agent, such asbenzene or cyclohexane, can alternatively be used. Membranes arecurrently under development which will enable separation of water fromethanol; these are reported to be nearly ready for commercialexploitation. Hence use of a membrane is another option available forseparating water from the ethanol rich stream.

Preferably the water content of the relatively dry ethanol produced instep (f) is less than about 5 mol %, and preferably less than about 2mol %.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be clearly understood and readilycarried into effect, a preferred form of plant for the production ofethyl acetate, and a process in accordance with the invention will nowbe described, by way of example only, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a flow diagram of a plant for the production of ethyl acetateconstructed to operate a process in accordance with the invention;

FIGS. 2 and 3 are triangular diagrams illustrating the boiling behaviourof ternary mixtures of ethanol, water and ethyl acetate at two differentpressures.

Referring to FIG. 1 of the drawings, it will be appreciated by thoseskilled in the art that, since the drawing is diagrammatic, manyconventional items of equipment, such as pumps, surge drums, flashdrums, heat exchangers, temperature controllers, pressure controllers,holding tanks, temperature gauges, pressure gauges, and the like, whichwould be required in an operating plant, have been omitted for the sakeof simplicity. Such items of equipment would be incorporated in anactual plant in accordance with standard chemical engineering practiceand form no part of the present invention. Moreover there are many waysof effecting heat exchange and the depiction of separate heat exchangerseach with its own heating or cooling line does not necessarily mean thatsingle heat exchanger units are necessary. Indeed in many cases it maybe more practicable and economic to use two separate heat exchangersinstead of one with a step change in temperature occurring in each. Itis also practicable to use conventional heat recovery techniques so asto recover heat from, or to increase the temperature of, one stream byheat exchange with another stream of the plant.

In the plant of FIG. 1 a stream of crude ethanol is pumped to the plantfrom a suitable holding tank (not shown) in line 1 at a pressure of 16.2bar absolute (16.2×10⁵ Pa) and at a temperature of approximately 30° C.and is admixed with recycled material from line 2. The resulting mixturein line 3 is heated by means of heat exchanger 4 to a temperature of166° C. thereby forming a vaporous stream which passes on in line 5 tobe mixed with a stream of hydrogen from line 6. The resulting mixturepasses on in line 7, is superheated in superheater 8 using high pressuresteam, and exits it in line 9 at a pressure of 14.8 bar absolute(14.8×10⁵ Pa) and at a temperature of 235° C. Line 9 leads to a firstdehydrogenation reactor 10 which contains a charge of a reduced copperoxide catalyst. A suitable catalyst is that sold under the designationE408Tu by Mallinckrodt Specialty Chemicals, Inc. In passage throughfirst dehydrogenation reactor 10 the mixture of ethanol and hydrogen ispartly converted by dehydrogenation according to equation (3) above toform ethyl acetate. This dehydrogenation reaction is endothermic.

The first intermediate dehydrogenation mixture exits reactor 10 in line11 at a temperature in the range of from 205° C. to 220° C. and isreheated in heater 12 under the influence of high pressure steam. Thereheated mixture flows on in line 13 to a second dehydrogenation reactor14 which also contains a charge of the same dehydrogenation catalyst asthat in reactor 10. Further dehydrogenation of ethanol to ethyl acetateoccurs in passage through second dehydrogenation reactor 14.

A second intermediate dehydrogenation mixture containing ethyl acetate,unreacted ethanol and hydrogen exits reactor 14 in line 15 and isreheated in reheater 16 which is heated by means of high pressure steam.The reheated stream flows on in line 17 to a third dehydrogenationreactor 18 which contains a charge of the same dehydrogenation catalystas is present in reactors 10 and 14.

The resulting third intermediate reaction mixture flows on in line 19 toheat exchanger 20 which is also heated by means of high pressure steam.The reheated mixture passes on in line 21 to fourth dehydrogenationreactor 22 which contains a further charge of the same dehydrogenationcatalyst that is loaded into the first, second and third dehydrogenationreactors 10, 14, and 18.

A crude product mixture exits fourth dehydrogenation reactor 22 in line23, is cooled in passage through a heat exchanger 24, and emerges inline 25 at a temperature of 60° C. and at a pressure of 11.3 bar(11.3×10⁵ Pa) absolute.

The crude product mixture in line 25 comprises hydrogen, ethyl acetate,unconverted ethanol, water and minor amounts of impurities presenteither from contamination in the feed or recycle streams or from sidereactions in reactors 10, 14, 18 and 22. Examples of these impuritiesinclude iso-propanol, acetaldehyde, diethyl ether, methanol, acetone,di-iso-propyl ether, n-butyraldehyde, butan-2-one, sec-butanol,iso-propyl acetate, pentan-2-one, n-butanol, sec-pentanol, sec-butylacetate, ethyl butyrate, n-butyl acetate and di-n-butyl ether. Ofparticular significance in relation to this invention are thoseimpurities whose boiling points are close to that of ethyl acetate orwhich form azeotropic mixtures with ethyl acetate. These includeethanol, as well as certain carbonyl-containing compounds such asacetone, acetaldehyde and butan-2-one.

The crude mixture in line 25 flows into a knockout pot 26 which isprovided with a condenser (not shown) supplied with chilled coolant. Theuncondensed gases, which are now at a temperature of −10° C., arerecovered in line 27. A part of these gases is recycled in line 28 andcompressed by means of gas recycle compressor 29 to a pressure of 15.5bar (1.55×10⁶ Pa) absolute to form the gas stream in line 6 for supplyto the first dehydrogenation reactor 10. Another part is taken in line30 for a purpose which will be described hereunder. A purge stream istaken in line 31.

The condensate is removed from knockout pot 26 in line 32 and is pumpedby a pump (not shown) to heat exchanger 33. The resulting re-heatedliquid, now at a temperature of 60° C. to 80° C., is fed via line 34 andmixed with a hydrogen-containing gas which is at a temperature of 119°C. and has been compressed by a second gas compressor 35 to a pressureof 43.1 bar (4.31×10⁶ Pa) absolute so as to pass along line 36. Theresulting mixture flows on in line 37 into a reactor 38 which contains acharge of a selective hydrogenation catalyst which is chosen so asselectively to hydrogenate reactive carbonyl-containing compounds, suchas n-butyraldehyde, butan-2-one and the like, to the respectivecorresponding alcohols but not to effect any significant hydrogenationof ethyl acetate to ethanol. The inlet temperature to reactor 37 isadjusted as necessary to a temperature in the range of from 60° C. to80° C. in dependance upon the degree of deactivation of the catalyst butis chosen to be as low as possible consistent with obtaining anacceptable reaction rate because the equilibrium is favourable at lowertemperatures than at high temperatures. A preferred catalyst is 5%ruthenium on carbon available from Engelhard.

The resulting selectively hydrogenated reaction product is nowessentially free from reactive carbonyl compounds, such as aldehydes andketones, and exits reactor 38, in admixture with unreacted hydrogen, inline 39 at a temperature of 70° C. to 90° C. This line leads to a lowerpart of a first distillation column 40 which is maintained at a ispressure of 1.5 bar (1×10⁵ Pa) absolute. A bottoms product is withdrawnfrom distillation column 40 in line 41. Part of this is recycled todistillation column through line 42, column reboiler 43 and line 44. Theremainder is passed by way of line 45 to a purification section (orwater removal package) 46 in which it is treated in any convenientmanner for the removal of water (and possibly other impurities)therefrom so as to yield a stream of moderately dry ethanol for recycleto the first dehydrogenation reactor 10 by way of line 2. The precisedesign of water removal package 46 will depend upon the composition ofthe ethanol feed stream in line 1. The bottoms product in line 41typically comprises mainly ethanol with minor amounts of, for example,iso-propanol, water, C₄₊ alkanols, and traces of ketones, other estersand ethers.

An overhead stream, which typically comprises a major proportion ofdiethyl ether and lesser amounts of other ethers, methanol, ethanol,n-butyraldehyde, and alkanes, as well as traces of acetaldehyde, ethylacetate, and water, is recovered in line 47 and condensed by means ofcondenser 48. Uncondensed gases are purged in line 49, while theresulting condensate is recycled to the top of distillation column 38 asa reflux stream in line 50. A side draw stream is taken fromdistillation column 40 in line 51 and pumped by a pump (not shown) to asecond distillation column 52 which is maintained at an overheadpressure of 12 bar (1.2×10⁶ Pa) absolute.

From the bottom of distillation column 52 a stream comprisingsubstantially pure ethyl acetate is recovered in line 53, part of whichis recycled to a lower part of distillation column 52 by way of line 54,column reboiler 55, and line 56. The remainder forms the product streamin line 57 from the plant; this can be taken to storage or furtherdistilled in one or more further distillation columns, if desired, inorder to remove minor amounts of iso-propyl acetate, di-propyl ether,and 1-ethoxybutane.

An overhead product consisting mainly of ethanol, ethyl acetate andwater, besides smaller amounts of 1-ethoxybutane, methanol, diethylether and di-propyl ether and traces of alkanes, is taken in line 58 andcondensed by means of condenser 59. The resulting condensate passes onin line 60, some being recycled to the first distillation column by wayof line 61 while the remainder is recycled as a reflux stream to thesecond distillation column 52 in line 62. Reference numeral 63 indicatesa line for recovery of water and other materials from water removalpackage 46.

The compositions in mol % of some of the more important streams in theplant of FIG. 1 are set out in Table 1 below.

TABLE 1 Stream 1 2 9 25 27 32 37 39 45 49 51 57 61 63 Hydrogen 0.00 0.001.96 32.43 95.67 0.24 5.32 3.26 0.00 64.41 0.00 0.00 0.00 0.00 Carbon0.00 0.00 0.01 0.17 0.49 0.00 0.03 0.03 0.00 0.64 0.00 0.00 0.00 0.00monoxide Water 0.13 0.13 0.13 1.20 0.04 1.80 1.71 1.73 2.26 0.93 3.940.00 5.36 39.80 Methanol 0.01 0.00 0.01 0.01 0.00 0.01 0.01 0.01 0.000.20 0.06 0.00 0.09 0.00 Ethanol 99.84 99.84 97.82 49.25 1.39 73.5069.67 72.70 96.52 16.76 50.42 0.02 68.73 37.90 Ethyl acetate 0.00 0.000.01 15.03 0.91 22.32 21.18 20.86 0.00 7.17 45.40 99.98 25.57 0.00Acetaldehyde 0.00 0.00 0.00 0.51 0.03 0.75 0.71 0.01 0.00 0.13 0.14 0.000.19 0.00 Ethane 0.00 0.00 0.00 0.09 0.20 0.03 0.04 0.04 0.00 0.82 0.000.00 0.00 0.00 Methane 0.00 0.00 0.03 0.41 1.17 0.03 0.09 0.09 0.00 1.780.00 0.00 0.00 0.00 Di-ethyl 0.01 0.00 0.01 0.27 0.09 0.37 0.35 0.360.00 7.09 0.04 0.00 0.06 0.00 ether n-butyralde- 0.00 0.00 0.00 0.010.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 hyde n-butanol 0.000.01 0.00 0.12 0.00 0.18 0.17 0.19 0.25 0.01 0.00 0.00 0.00 4.53sec-butanol 0.00 0.01 0.00 0.26 0.00 0.38 0.36 0.51 0.67 0.05 0.00 0.000.00 12.15 Butan-2-one 0.01 0.00 0.01 0.10 0.01 0.14 0.14 0.00 0.00 0.000.00 0.00 0.00 0.00 n-butyl acetate 0.00 0.00 0.00 0.05 0.00 0.08 0.070.07 0.10 0.01 0.00 0.00 0.00 1.81 sec-butyl 0.00 0.00 0.00 0.02 0.000.03 0.03 0.03 0.04 0.00 0.00 0.00 0.00 0.73 acetate Ethyl butyrate 0.000.00 0.00 0.04 0.00 0.07 0.06 0.06 0.09 0.00 0.00 0.00 0.00 1.63Di-butyl ether 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.000.00 0.00 0.18 n-hexanol 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.010.00 0.00 0.00 0.00 0.18 iso-butanol 0.00 0.01 0.01 0.01 0.00 0.01 0.010.01 0.01 0.00 0.00 0.00 0.00 0.18 Others 0.00 0.00 0.00 0.02 0.00 0.040.03 0.03 0.04 0.00 0.00 0.00 0.00 0.91 Total 100.00 100.00 100.00100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00100.00

FIG. 2 is a triangular diagram illustrating the distillationcharacteristics of mixtures of ethanol, water and ethyl acetate at 760mm Hg (1.01×10⁶ Pa) in which are plotted distillation lines fordifferent mixtures of the three components. FIG. 3 is a similar diagramillustrating the distillation characteristics of the same ternary systemat 9308 mm Hg (12.41×10⁶ Pa). It will be noted that there aresignificant differences between the distillation lines observed atdifferent operating pressures. In FIG. 2 the composition of a typicalfeed as might be supplied in line 39 of the plant of FIG. 1 is indicatedby point A. Point B indicates the composition of the side draw stream inline 51 for this feed. Point C indicates the composition of theresulting bottom stream in line 41 and point D indicates the compositionof the stream in line 61. The effective feed composition to column 40lies on the intersection of the straight line joining A and D with thestraight line joining points B and C. In FIG. 3 the points B and Drepresents the same compositions as the corresponding points in thetriangular diagram of FIG. 2. Point E represents the composition of thesubstantially pure ethyl acetate recovered in line 45.

The invention is further described in the following Examples.

EXAMPLES 1 to 5

These Examples investigated the dehydrogenation of ethanol to ethylacetate in the presence of hydrogen. The apparatus used included adehydrogenation reactor made of stainless steel tubing which contained acharge of reduced copper oxide catalyst and which was immersed in a hotoil bath for heating purposes.

At start-up a charge of 200 ml of a tabulated copper oxide catalystavailable under the designation E408Tu from Mallinckrodt SpecialtyChemicals was placed in the reactor which was then purged with nitrogenat 14.5 bar (14.5×10⁵ Pa). A dilute H₂ in N₂ gaseous mixture at 3 bar(3×10⁵ Pa) was passed over the catalyst at a rate of 600 standard litersper hour for 60 hours in order to effect catalyst reduction. The oilbath was raised to the temperature indicated in Table 2 below. The gasfeed was then changed to pure hydrogen.

In operation hydrogen was introduced to the dehydrogenation reactor at arate of 2 standard liters per hour by way of a pressure regulator andflow controller through a line which was immersed in the bottom of theoil bath. An ethanol stream whose composition is set out in Table 2 wasfed as a liquid at a rate of 200 ml/hr to a vaporiser and mixed with thehydrogen. The resulting vaporous mixture of ethanol and hydrogen wassupplied to the dehydrogenation reactor.

The reaction products were cooled and the liquid condensate was analysedby gas chromatography. The results obtained are summarised in Table 2.

TABLE 2 Example No Feed 1 2 3 4 5 Temperature — 225 224 224 223 224 (°C.) Pressure — 4.53 2.74 7.91 28.6 47.0 (bar)[10⁵Pa] Product Analysis(wt %) Acetaldehyde 0.007 2.578 5.317 1.388 0.114 0.027 Methanol 0.0640.063 0.087 0.034 0.013 0.011 Di-ethyl ether 0.108 0.133 0.120 0.1390.167 0.185 Ethanol 95.093 63.184 66.778 64.050 67.236 72.676 Acetone0.007 2.264 2.883 1.679 0.630 0.326 iso-propanol 3.403 1.582 1.081 2.1143.210 3.511 Di-iso-propyl 0.116 0.139 0.134 0.138 0.136 0.138 ethern-butyral- 0 0.012 0.010 0.006 0.004 0.005 dehyde Ethyl acetate 0.03025.605 18.935 27.087 26.377 21.107 Butan-2-one 0.005 1.230 1.655 0.6610.074 0.015 sec-butanol 0.004 0.768 0.543 0.761 0.360 0.174 iso-propyl 00.184 0.144 0.040 0.316 0.318 acetate Pentan-2-one 0 0.316 0.309 0.2330.055 0.010 n-butanol 0.097 0.329 0.410 0.274 0.203 0.431 sec-pentanol 00.138 0.075 0.180 0.148 0.087 sec-butyl 0 0.058 0.037 0.057 0.052 0.044acetate Ethyl butyrate 0 0.132 0.115 0.093 0.030 0.075 n-butyl acetate 00.123 0.096 0.086 0.022 0.076 Water 0.540 0.789 0.920 0.660 0.450 0.460Others 0.526 0.373 0.351 0.320 0.403 0.324 Total 100.00 100.00 100.00100.00 100.00 100.00

EXAMPLES 6 to 9

In these Examples the selective hydrogenation of reactive carbonylcompounds in the presence of ethyl acetate was investigated using ahydrogenation reactor constructed out of stainless steel which wasimmersed in a hot oil bath for heating purposes.

In operation hydrogen was introduced by way of a pressure regulator andflow controller to the reactor which contained a charge of an Englehard5% ruthenium on carbon granular catalyst.

At start up a charge of 100 ml of the granular catalyst was placed inthe reactor which was then supplied with hydrogen at a pressure of 7.9bar (7.9×10⁵ Pa), and warmed to 180-200° C. from room temperature at arate of 20° C per hour. The reactor was held at 180-200° C. for one hourand then cooled. At the end of this procedure the catalyst was fullyreduced.

Dehydrogenation reaction product mixture whose composition is set outunder “Feed” in Table 3 was introduced to a heater at a rate of 130ml/hr and admixed with 7.8 standard liters per hour of hydrogen prior toadmission to the selective hydrogenation reactor. The reaction productwas cooled and the liquid condensate was analysed by gas chromatography.The results are summarised in Table 3.

TABLE 3 Example No Feed 6 7 8 9 Reactor Temperature — 91 80 72 110 (°C.) Pressure (bar)[10⁵Pa] — 14.2 14.2 14.4 14.1 Product Analysis (Wt %)Acetaldehyde 0.904 0.034 0.040 0.038 0.039 Diethyl ether 0.579 0.4280.418 0.417 0.419 Ethanol 68.223 70.040 70.121 70.163 70.301 Acetone2.282 trace trace trace trace iso-propanol 1.004 3.232 3.233 3.213 3.231Di-iso-propyl ether 0.003 0.098 0.097 0.097 0.097 n-butyraldehyde 0.010trace trace trace trace Ethyl acetate 23.263 22.572 22.464 22.437 22.396Butan-2-one 0.170 0.002 0.004 0.007 0.003 sec-butanol 0.371 0.567 0.5660.560 0.567 iso-propyl acetate 0.186 0.185 0.184 0.184 0.184 n-butanol0.507 0.730 0.770 0.776 0.570 Water 1.410 1.170 1.170 1.200 1.270 Others1.088 0.942 0.933 0.908 0.923 Total 100.00 100.00 100.00 100.00 100.00Notes: The increased amount of n-butanol noted in Examples 6 to 9compared with the amount in the feed can be ascribed not only ton-butanol formed by hydrogenation of n-butyraldehyde present in the feed(the amount of which is, in any case, difficult to measure) but alsofrom hydrogenation of other products which contain C₄ groups and whichare included in the figure given for “others” in the feed.

EXAMPLES 10 to 12

The general procedure of Examples 6 to 9 was repeated using a differentfeed and different reaction conditions. The results are set out in Table4 below.

TABLE 4 Example No Feed 10 11 12 Reactor Temperature (° C.) — 79 98 119Pressure (bar) [10⁵ Pa] — 42.6 42.1 42.5 Product Analysis (Wt %)Acetaldehyde 0.952 0.006 0.006 0.006 Diethyl ether 0.030 0.030 0.0290.033 Ethanol 64.703 65.930 66.034 65.627 Acetone trace 0 0 0iso-propanol 0.022 0.032 0.035 0.038 n-butyraldehyde trace 0 0 0 Ethylacetate 31.692 31.410 31.155 31.409 Butan-2-one 0.301 trace trace 0.001sec-butanol 0.487 0.803 0.806 0.810 n-butanol 0.560 0.588 0.596 0.573Water 0.620 0.600 0.700 0.890 Others 0.633 0.601 0.639 0.613 Total100.00 100.00 100.00 100.00

EXAMPLE 13

A mixture containing ethanol, water, ethyl acetate and other componentswas distilled in a continuous feed laboratory distillation apparatushaving the general layout of columns 40 and 52 of FIG. 1, except thatline 51 received condensate from line 50, rather than a side draw streamfrom an outlet positioned somewhat lower in column 40. A bleed of 0₂-free nitrogen was supplied to column 40 so as to ensure that oxygenwas excluded from column 40 in order to prevent oxidation of anyoxygen-sensitive components in the feed in line 39 such as aldehydes.Hence column 40 was operated at a few millibars over atmosphericpressure. The feed to column 30 was vaporised in a stream of O₂-freenitrogen prior to introduction into column 40. The reflux temperature incolumn 40 was 64° C., the overhead temperature was 72° C. and thetemperature at the bottom of the column was 73° C. The reflux ratio was5:1. The operating pressure in column 52 was 12.4 bar (1.24×10⁶ Pagauge). The overhead temperature was 160° C., the reflux temperature was153° C. and the boiler temperature was 204° C. The reflux ratio was2.8:1. The distillation column had 3 thermocouples positioned near thetop, at the mid point and near the bottom, the readings of which were163° C., 180° C. and 180° C. respectively. The results obtained arelisted in Table 5 in which amounts are in % by weight.

TABLE 5 Line No. 39 51 41 61 53 Acetaldehyde 0.009 0.007 0.013 0.446Methanol 0.090 0.141 0.199 Diethyl ether 0.073 0.113 0.226 Ethanol57.626 31.077 96.579 71.382 0.064 iso-propanol 0.027 0.087 Ethyl acetate40.514 68.021 0.018 24.811 99.890 Butan-2-ol 0.548 1.499 n-butanol 0.1920.021 0.519 0.010 Ethyl butyrate 0.117 0.307 Butyl acetate 0.136 0.358Water 0.550 0.590 0.330 2.920 0.010 “Light” unknowns 0.020 0.029 0.003“Heavy” unknowns 0.098 0.001 0.290 0.013 0.026 Total 100.00 100.00100.00 100.00 100.00

What is claimed is:
 1. A process for the production of ethyl acetatewhich comprises: (a) converting a C₂ feedstock comprising ethanol toethyl acetate in an ethyl acetate production zone by a procedureselected from: (i) dehydrogenation, and (ii) reaction with acetaldehyde(b) recovering from the ethyl acetate production zone an intermediatereaction product mixture comprising hydrogen and liquefiable productscomprising the majority of the ethyl acetate produced in step (a),ethanol, and by-products containing reactive carbonyl groups; (c)passing at least a portion of the liquefiable products of theintermediate reaction product mixture as recovered from the ethylacetate production zone to a selective hydrogenation zone and contactingthe liquefiable products of the intermediate reaction product mixturewith a selective hydrogenation catalyst in the presence of hydrogen inthe selective hydrogenation zone maintained under selectivehydrogenation conditions effective to selectively hydrogenate saidby-products containing reactive carbonyl groups to correspondingalcohols; (d) recovering from the selective hydrogenation zone aselectively hydrogenated reaction product mixture comprising ethylacetate, ethanol, hydrogen and hydrogenated by-products comprising saidcorresponding alcohols; (e) distilling the selectively hydrogenatedreaction product mixture in one or more distillation zones so as toproduce a first composition comprising substantially pure ethyl acetateand a second composition comprising ethanol and water; (f) treating thesecond composition of step (e) to separate water therefrom and yield athird composition comprising ethanol with a reduced water content; and(g) recovering the third composition of step (f).
 2. A process accordingto claim 1, wherein in step (a) the C₂ feedstock is converted to ethylacetate by a dehydrogenation procedure which comprises contacting avaporous mixture containing ethanol and hydrogen with a dehydrogenationcatalyst in a dehydrogenation zone maintained under dehydrogenationconditions effective for dehydrogenation of ethanol to yield ethylacetate.
 3. A process according to claim 2, wherein the ethanol:hydrogenmolar ratio in the dehydrogenation zone is from about 1:10 to about1000:1, the combined partial pressure of ethanol and hydrogen in thedehydrogenation zone is from about 3 bar (3×10⁵ Pa) up to about 50 bar(5×10⁶ Pa), and the temperature in the dehydrogenation zone is fromabout 100° C. to about 260° C.
 4. A process according to claim 3,wherein the combined partial pressure of ethanol and hydrogen in thedehydrogenation zone is at least about 6 bar (6×10⁵ Pa) up to about 30bar (3×10⁶ Pa).
 5. A process according to claim 2, wherein thedehydrogenation catalyst is a copper containing catalyst whichcomprises, before reduction, copper oxide on alumina.
 6. A processaccording to claim 2, wherein the rate of supply of the C₂ feedstock tothe dehydrogenation zone corresponds to an ethanol liquid hourly spacevelocity (LHSV) of from about 0.5 hr⁻¹ to about 1.0 hr⁻¹.
 7. A processaccording to claim 1, wherein the selective hydrogenation conditions inthe selective hydrogenation zone of step (c) include a reaction productmixture:hydrogen molar ratio of from about 1000:1 to about 1:1, acombined partial pressure of the liquefiable products of theintermediate reaction product mixture and hydrogen of from about 5 bar(5×10⁵ Pa) to about 80 bar (8×10⁶ Pa), and a temperature in the range offrom about 20° C. to about 160° C.
 8. A process according to claim 1,wherein the combined partial pressure of the liquefiable products of theintermediate reaction product mixture and hydrogen in step (C) is fromabout 25 bar (2.5×10⁶ Pa) to about 50 bar (5×10⁶ Pa).
 9. A processaccording to claim 1, wherein the selective hydrogenation catalystcomprises a metal selected from nickel, palladium, platinum, ruthenium,rhodium and rhenium.
 10. A process according to claim 9, wherein thecatalyst comprises ruthenium on carbon.
 11. A process according to claim1, wherein the rate of supply of liquefiable liquid products of theintermediate reaction product mixture to the selective hydrogenationzone corresponds to a liquid hourly space velocity (LHSV) of from about0.5 hr⁻¹ to about 2.0 hr³¹ ¹.
 12. A process according to claim 1,wherein step (e) comprises supplying the selectively hydrogenatedreaction product mixture to a first distillation zone maintained underdistillation conditions effective for distillation therefrom of a firstdistillate comprising ethanol, water and ethyl acetate, recovering afirst distillate comprising ethanol, water and ethyl acetate from thefirst distillation zone and a bottom product comprising ethanol andwater, supplying the first distillate to a second distillation zonemaintained under distillation conditions effective for distillationtherefrom of a second distillate comprising ethanol, water, and ethylacetate and so as to yield a substantially pure ethyl acetate bottomproduct, and recovering a substantially pure ethyl acetate bottomproduct from the second distillation zone.
 13. A process according toclaim 12, wherein the first distillation zone is operated at a pressureof less than about 4 bar (4×10⁵ Pa).
 14. A process according to claim12, wherein the first distillation zone is operated at a pressure offrom about 1 bar (10⁵ Pa) to about 2 bar (2×10⁵ Pa).
 15. A processaccording to claim 12, wherein the second distillation zone is operatedat a pressure of from about 4 bar (4×10⁵ Pa) to about 25 bar (2.5×10⁶Pa).
 16. A process according to claim 12, wherein the seconddistillation zone is operated at a pressure of from about 9 bar (9×10⁵Pa) to about 15 bar (1.5×10⁶ Pa).
 17. A process according to claim 12,wherein the first distillate contains less than about 10 mol % water.18. A process according to claim 12, wherein an ethanol rich streamcontaining substantially all of the water in the selectivelyhydrogenated reaction product mixture is recovered from the bottom ofthe first distillation zone, while an overhead stream that containslight components having lower boiling points than ethyl acetate and itsazeotropes with water and ethanol present in the selectivelyhydrogenated reaction product mixture is recovered from the firstdistillation zone, and in which the first distillate comprises a liquiddraw stream which is recovered from an upper region of the firstdistillation zone and which comprises ethyl acetate, ethanol, water andminor amounts of other components.
 19. A process according to claim 18,wherein the liquid draw stream contains from about 40 mol % to about 55mol % ethyl acetate, from about 1 mol % to about 6 mol % water, not morethan about 1 mol % other components, and the balance ethanol.
 20. Aprocess according to claim 19, wherein the liquid draw stream containsabout 45 mol % ethyl acetate, about 50 mol % ethanol, about 4 mol %water and about 1 mol % other components.
 21. A process according toclaim 18, wherein the liquid draw stream is passed to the seconddistillation zone which is operated at a pressure of from about 4 bar(4×10⁵ Pa) absolute to about 25 bar (2.5×10⁶ Pa) absolute.
 22. A processaccording to claim 21, wherein the bottom product from the seconddistillation zone contains from about 99.8 mol % to about 99.95 mol %ethyl acetate.
 23. A process according to claim 20, wherein the seconddistillate comprises the overhead stream from the second distillationzone and is returned to the first distillation zone.
 24. A processaccording to claim 23, wherein the overhead stream from the seconddistillation zone contains about 25 mol % ethyl acetate, about 68 mol %ethanol, about 6 mol % water, and about 1 mol % of other components. 25.A process according to claim 23, wherein the overhead stream from thesecond distillation zone is returned to the first distillation zone at apoint above the feed point of the liquefiable products of theselectively hydrogenated reaction product mixture.
 26. A processaccording to claim 18, wherein in step (f) the ethanol rich streamrecovered from the bottom of the first distillation zone is subjected totreatment for the removal of water therefrom thereby to produce arelatively dry ethanol stream suitable for recycle to step (a).
 27. Aprocess according to claim 1, wherein the relatively dry ethanol streamof step (f) is recycled to step (a).
 28. A process according to claim 1,wherein step (e) comprises extractive distillation with an extractiveagent comprising polyethylene glycol and dipropylene glycol, diethyleneglycol, or triethylene glycol.
 29. A process according to claim 1,wherein step (e) comprises extractive distillation in the presence of anextractive agent containing dimethyl sulphoxide.